I. Field of the Invention
The present invention relates to a method and apparatus for controlling data transfer between two stations.
II. Description of the Related Art
IS-95 is an over-the-air interface standard which, together with its derivatives such as IS-95-A, IS-99 and IS-707, IS-657 and ANSI J-STD-008 etc. (referred to herein collectively as the IS-95 standards), defines an interface for implementing a digital personal communication system using code division multiple access (CDMA) signal processing techniques. A personal communication system configured substantially in accordance with the use of IS-95 is described in U.S. Pat. No. 5,103,459 entitled xe2x80x9cSystem and Method for Generating Signal Waveforms in a CDMA Personal communication Systemxe2x80x9d assigned to the assignee of the present invention and incorporated herein by reference.
FIG. 1 is a schematic diagram representing a personal communication system configured in accordance with IS-95. As is typical for most personal communication systems, IS-95 allows mobile telephone service to be provided to a set of wireless stations or terminals 10 (typically cellular telephones or xe2x80x9cmobilesxe2x80x9d) using a set of base transceiver stations (BTS) 12 coupled by a base station controller (BSC) 14 and a mobile switching center (MSC) 16 to a public switched telephone network (PSTN) 18. During a call from a wireless terminal 10, the terminal 10 interfaces with one or more base stations 12 in a communications link using CDMA modulated radio frequency (RF) signals. The RF signal transmitted from the base station 12 to the wireless terminal 10 is referred to as the forward link, and the RF signal transmitted from the wireless terminal 10 to the base station 12 is referred to as the reverse link.
Under the IS-99 and IS-707 standards (referred to hereinafter simply as IS-707), an IS-95 compliant communications system can also provide data communications services. Data communications services allow digital data to be exchanged using a wireless terminal 10 and the RF interface to one or more base stations 12. Examples of the type of digital data typically transmitted using the IS-707 standard include computer files and electronic mail. Under IS-95A and IS-707, frames are transmitted once every 20 mS (milliseconds).
The IS-95B Standard has recently been developed to enable multiple traffic channels to be assigned to a wireless terminal by a base station in a communications link in both forward and reverse directions. IS-95B defines formats for supplemental traffic channels for different rate sets, but is silent as to how supplemental channels should be assigned in the communications link. There are only a finite number of traffic channels and, as such, the channels are a limited resource. Furthermore, it is not unusual in the transfer of data for the rate at which the data is delivered to vary with time. At some times the data rate may be relatively high and at others relatively low, the delay tolerances of several data sources is not rigid. It is wasteful of resources simply to assign a maximum number of channels to a communications link in order to ensure that the link is able to match the rate at which data is transferred with the maximum rate at which data may be delivered for transfer over the link.
The invention aims to overcome or at least minimize some of the above discussed disadvantages and problems.
The invention will be described in the following with reference to a CDMA system in which the invention may be embodied. A CDMA system is preferred because of the advantages that such a system offers over other communications systems. The invention is, however, not limited to being embodied in a CDMA system and can be applied equally to any communications system in which plural channels may be assigned in a communications link.
In one aspect the invention provides an apparatus for controlling data transfer between two stations, the apparatus comprising: a link manager for controlling allocation of available channels in a plurality of communications links in each of which communications links data is transferred between two stations in at least one channel; a data buffer for buffering data from a data source; and a controller for determining a parameter representing the buffering of data in the buffer and for generating a request for a change in the allocation of channels in a communications link between two stations depending on the parameter, and wherein the link manager is responsive to a request generated by the controller to allocate a different number of channels to the communications link or to generate a refusal of the request.
In another aspect the invention provides a method of controlling data transfer between two stations, the method comprising: controlling allocation of available channels in a plurality of communications links in each of which communications links data is transferred between two stations in at least one channel; buffering data from a data source; determining a parameter representing the buffering of data in the buffer; generating a request for a change in the allocation of channels in a communications link between two stations depending on the parameter; and responding to a generated request by allocating a different number of channels to the communications link or generating a refusal of the request.